Windshielding structure for an antenna

ABSTRACT

A windshielding structure for a large-diameter high-frequency dish-type antenna includes a flexible membrane extending from the edge of the antenna dish to a fixed rigid member mounted on a base plane. The membrane permits controlled movement of the antenna dish in azimuth and elevation, but minimizes the effect of wind approaching the dish from the front direction (head-on wind) by preventing the wind from interacting with the antenna dish edge to cause Von Karman vortices and associated mechanical oscillations of the antenna. The enclosure formed behind the antenna dish by the membrane, the antenna dish, the fixed rigid member and the base plane can be used for protection of equipment and personnel. The fixed rigid member may have a lip protruding from its surface to divert from the dish and membrane, wind approaching the antenna dish from other directions.

iii-P 75 GR 399189065 United States Patent [1 1 [111 3,918,065 Hutchisonet al. Nov. 4, 1975 WINDSHIELDING STRUCTURE FOR AN 57 I ABSTRACT ANTENNA[75] Inventors: Paul Trice Hutchison, Rumson; John William McCulloch, Frhold, b th A windshielding structure for a large-diameter highof NJ.frequency dish-type antenna includes a flexible membrane extending fromthe edge of the antenna dish to [73] Asslgnee a z z i g gfi fi J a fixedrigid member mounted on a base plane. The

rpora u 1 membrane permits controlled movement of the an- [22] Filed:Apr. 19, 1974 tenna dish in azimuth and elevation, but minimizes theeffect of wind approaching the dish from the front di- [211 Appl 462351rection (head-on wind) by preventing the wind from interacting with theantenna dish edge to cause Von [52] US. Cl 343/872; 343/704 Karmanvortices and associated mechanical oscilla- [51] Int. Cl. ...l H0lb 1/42tions f h n enna. Th enclosure formed ehin he [58] Field of Search343/872, 840, 704 antenna dish by the membrane, the antenna dish, thefixed rigid member and the base plane can be used for [56] ReferencesCited protection of equipment and personnel. The fixed UNITED STATESPATENTS rigid member may have a lip protruding from its surface todiventIfrom the dish and membrane, wind ap- 8 40 W gig 5: I proachmgtheamenna diSh from other directions. 3,820,118 6/1974 Hall 343/872Primary Examiner-Eli Lieberman Attorney, Agent, or Firm-David L.Hurewitz; E. W. Adams, Jr.

-9iOlnims, 3 Drawing Figures U.S. Patent Nov. 4, 1975 Sheet 1 of23,918,065

FIG.

FIG. 2

U.S. Patent Nov. 4, 1975 Sheet 2 of 2 3,918,065

WINDSHIELDING STRUCTURE FOR AN ANTENNA BACKGROUND OF THE INVENTION dishfrom undesired mechanical oscillations caused by 7 wind.

As is well known, large-diameter parabolic-dish antennas used, forexample, in high-frequency satellite systems are difficult to stabilizemechanically in the presence of wind. This difficulty is in part due totheir large size and in part due to the requirement of dish movement inazimuth and elevation to properly track a satellite.

Attempts have been made to shield such antenna dishes with well-knownradome type structures. Such radomes completely surround the antennadish at all times, thereby protecting the dish from wind. However, anyrainfall on the radome can cause unacceptable attenuation of bothtransmitted and received high-fre' quency signals. Other dome structuresare designed with a window which is opened only when the antenna isbeing used. However, while such an open-window dome structure shieldsthe antenna from winds approaching the antenna dish from the rear, itprovides minimal protection from winds approaching the dish from thefront (head-on winds). Thus, an antenna dish so protected may not beeffectively used for tracking when head-on winds occur.

SUMMARY OF THE INVENTION In accordance with the present invention, arigid windshielding member surrounds an antenna dish but has an openingcorresponding to, and slightly larger than the antenna dish. The antennaand shielding structure is mounted on the ground or a base plane. Aflexible membrane extends from the entire edge of the dish to the rigidmember. This rigid member may, for example, be of the space frame orgeodesic type, but it may alternatively be made of flexible material andmaintained in a relatively rigid position by controlling the airpressure within an enclosure bounded by the antenna dish, the flexiblemembrane, the relatively rigid member and base plane.

Head-on wind striking the vicinity of the edge of the dish is guided bythe flexible membrane away from the dish edge to the rigid member overwhich the wind is shed. The flexible membrane prevents the interactionof wind with the antenna dish edge thereby minimizing mechanicaloscillations of the dish. In addition, a lip may be added protrudingfrom the rigid structure to further protect the membrane and dish.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a longitudinal side viewof the windshielding structure in accordance with the invention;

FIG. 2 shows a head-on view of the structure of FIG. 1; and

FIG. 3 shows a perspective view of the embodiment of the invention ofFIGS. 1 and 2.

DETAILED DESCRIPTION The invention is shown in FIG. 1 in a lonitudinalsectional side view, in FIG. 2 in a head-on view and in FIG.

3 in a perspective view. In all figures, identical reference numbersindicate identical structures. A dish antenna 10 is supported bymounting structure 19 which rests on base plane 12. Feeding andtransmission structures are not shown. A curved member 13 extends upwardfrom the base plane 12 to surround the antenna except for an opening 17dimensioned and positioned so thatthe transmission to and from the dish10 passes through the opening. Lip 14 surrounding the opening 17 andprotruding from member 13 may be added to further protect the antennadish 10 from wind approaching the antenna from the rear, side and top.This curved member 13 and its lip 14 may be made of any material. It isnot, however, necessary for member 13 to be curved as shown. This rigidmember may, for example, be of the space frame or geodesic type and isgenerally fixed in shape. It may, however, be flexible and maintained inposition by controlling the air pressure from within. An annularflexible membrane 15 is attached to the entire edge 11 of the dishantenna and to the curved structure 13 at the edge of the opening 17(the base of lip 14 if the lip is present). This flexible membrane may,for example, be made of elastomeric material such as neoprene and maytypically be oneeighth to one-fourth inch thick. The dish and membranetogether occupy the opening 17 in the curved member 13. Thus, anenclosure 18 is formed by the dish antenna 10, the membrane 15, curvedstructure 13 and base plane 12. 1

Von Kannan vortices, as is well known, are alternate Whirlpools offluid, such as air, which are shed from a surface when the fluidinteracts with the surface edge. The interaction of wind with antennadish edges produces Von Karman vortices. These vortices are shedalternately from opposite regions on the edges of the antenna dish andinduce mechanical oscillations which, in turn, produce pointing andtracking errors.

It is the object of the invention to minimize oscillations due to theseVon Karman vortices by preventing the wind from interacting with theantenna dish edge. Membrane 15 serves to divert head-on wind away fromthe antenna dish edge to the curved member 13 and over lip 14 ifpresent. Lip 14 further serves to divert winds, approaching the antennadish from all other directions, away from the antenna dish edge. Thecurved member 13 and lip 14 need not be completely rigid because anymechanical oscillations induced in these structures by the diverted windor other force can not be transmitted back to the antenna dish since theflexibility of membrane 15 damps such oscillations. Communicationssatellites normally move slightly relative to the earths surface.Because the width of the received high frequency signal beam is small,motion of the satellite relative to the earth may cause an interruptionin communications. It is therefore necessary that the antenna dish notbe fixed in position but be subject to controlled movement to track thesatellite. Because the membrane is flexible, desired movement inelevation and azimuth is permitted to properly track a communicationsatellite and avoid interruption in communications.

The dish is not physically covered but rain falling directly onto theantenna dish does not cause serious attenuation of the signaltransmitted or receive'd because the total electric field at the surfaceof the reflecting metal is almost zero. This field at the surface isnearly null because the incident wave on the surfaEE and the reflectedwave from the surface are almdt equal in 3 magnitude and 180 out ofphase at the surface.

The invention thus reduces difficulties associated with both attenuationof signal due to presence of a radome and head-on winds thereby enablingthe antenna dish to be used in severe weather conditions.

ln all cases it is to be understood that the above describedarrangements are merely illustrative of a small number of the manypossible applications of the principles of the invention. Numerous andvaried other arrangements in accordance with these principles mayreadily be devised by those skilled in the art without departing fromthe spirit and scope of the invention.

What is claimed is:

l. A windshielding antenna structure comprising a parabolic section dishantenna mounted on a base plane, a structure surrounding the antennadish but having an opening corresponding to and slightly larger than theantenna dish, said structure being positioned so that electric wavesreflected from the dish pass through the opening of said structure, aflexible membrane extending from the entire edge of said antenna dish tothe opening of said structure whereby head-on wind is diverted from theedge of said antenna dish to said structure thereby preventingmechanical oscillations of said antenna dish due to wind, said dishbeing capable of controlled movement relative to said structuresurrounding said antenna dish.

2. A structure as described in claim 1 wherein a lip protrudes from thesurrounding structure so that wind is diverted by the lip away from themembrane and the dish edge.

3. A structure as described in claim 1 wherein an enclosure is formedbounded by the antenna dish, the surrounding structure, the membrane andthe base plane.

4. A windshielded antenna structure comprising a parabolic section dishantenna mounted on a base plane, a fixed member mounted on the baseplane extending behind and above said antenna, a flexible membraneextending from the entire edge of said antenna dish to said fixed memberwhereby head-on wind is diverted from the edge of said antenna dish tosaid fixed member thereby minimizing mechanical oscillations of saidantenna dish said dish being capable of controlled movement relative tosaid structure surrounding the antenna dish.

5. A structure as described in claim 1 wherein a lip protrudes from thefixed member so that wind is diverted by the lip away from the membraneand the dish edge.

6. A structure as described in claim 4 wherein an enclosure is formed bysaid antenna dish, said fixed member, said membrane and the base plane.

7. An improved parabolic section dish antenna windshield mounted on abase plane and having a fixed structure extending behind and above anantenna whereby the antenna is shielded from winds behind and above theantenna wherein the improvement comprises a flexible membrane connectedfrom the entire edge of said antenna to said fixed structure wherebyhead-on wind is diverted from theedge of said antenna to said fixedstructure and prevented from interacting with the antenna edge to causemechanical oscillations of said antenna said dish being capable ofcontrolled movement relative to said structure surrounding the antennadish.

8. A windshield as described in claim 7 wherein a lip protrudes from thefixed member so that wind is diverted by the lip away from the membraneand the dish edge.

9. A windshield as described in claim 7 wherein an enclosure is formedby said antenna dish, said fixed member, said membrane and the baseplane.

1. A windshielding antenna structure comprising a parabolic section dishantenna mounted on a base plane, a structure surrounding the antennadish but having an opening corresponding to and slightly larger than theantenna dish, said structure being positioned so that electric wavesreflected from the dish pass through the opening of said structure, aflexible membrane extending from the entire edge of said antenna dish tothe opening of said structure whereby head-on wind is diverted from theedge of said antenna dish to said structure thereby preventingmechanical oscillations of said antenna dish due to wind, said dishbeing capable of controlled movement relative to said structuresurrounding said antenna dish.
 2. A structure as described in claim 1wherein a lip protrudes from the surrounding structure so that wind isdiverted by the lip away from the membrane and the dish edge.
 3. Astructure as described in claim 1 wherein an enclosure is formed boundedby the antenna dish, the surrounding structure, the membrane and thebase plane.
 4. A windshielded antenna structure comprising a parabolicsection dish antenna mounted on a base plane, a fixed member mounted onthe base plane extending behind and above said antenna, a flexiblemembrane extending from the entire edge of said antenna dish to saidfixed member whereby head-on wind is diverted from the edge of saidantenna dish to said fixed member thereby minimizing mechanicaloscillations of said antenna dish said dish being capable of controlledmovement relative to said structure surrounding the antenna dish.
 5. Astructure as described in claim 1 wherein a lip protrudes from the fixedmember so that wind is diverted by the lip away from the membrane andthe dish edge.
 6. A structure as described in claim 4 wherein anenclosure is formed by said antenna dish, said fixed member, saidmembrane and the base plane.
 7. An improved parabolic section dishantenna windshield mounted on a base plane and having a fixed structureextending behind and above an antenna whereby the antenna is shieldedfrom winds behind and above the antenna wherein the improvementcomprises a flexible membrane connected from the entire edge of saidantenna to said fixed structure whereby head-on wind is diverted fromthe edge of said antenna to said fixed structure and prevented frominteracting with the antenna edge to cause mechanical oscillations ofsaid antenna said dish being capable of controlled movement relative tosaid structure surrounding the antenna dish.
 8. A windshield asdescribed in claim 7 wherein a lip protrudes from the fixed member sothat wind is diverted by the lip away from the membrane and the dishedge.
 9. A windshield as described in claim 7 wherein an enclosure isformed by said antenna dish, said fixed member, said membrane and thebase plane.